The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Advanced diesel combustion modes employing high exhaust gas recirculation (EGR) rates and advanced injection strategies may be utilized for meeting emission regulations. Advanced injection strategies can include premixed charge compression ignition (PCCI) and homogeneous charge compression ignition (HCCI). Advanced diesel combustion modes can further include limited temperature combustion (LTC). It is understood that premixed combustion noise can reach unacceptable levels in the presence of high EGR rates and injection inaccuracy.
It is known, for example, to impose limits for air and/or fuel during base engine calibration to control engine noise. However, these limits are inherently conservative and sacrifice efficiency. Further, it is known to utilize analog combustion noise meters and/or dedicated combustion analysis tools during combustion calibration to compute acoustic combustion noise measures based on frequency spectrum analysis of in-cylinder pressure measurements. Although combustion noise meters and analysis tools can be useful during engine calibration, they may not be practically directly usable for on-board vehicle applications for real-time closed-loop control due, for example, to hardware cost or computational throughput requirements